Invertebrate Abundance and Rate of Decomposition in Beach Wrack of Zostera marina and Fucus distichus

Abstract

Beach ecosystems rely on the supply of off-site primary production in the form of stranded algae, or beach wrack. As beach wrack washes up on shore, it is colonized by a host of microbes, detrivores and herbivores, which supply the beach ecosystem food web. This study seeks to understand how nutrients are transferred from seaweed throughout the food web by looking at how mass loss changes in beach wrack as larger invertebrates are included or excluded from the system. We found more total colonizers of beach wrack in treatments that included larger invertebrates. The community structure of colonizers shifted with site, and in treatments that included large amphipods there was more mass loss of algae due to herbivory. In wrack with more ephydridae larvae, mass loss was more uniform between treatments. This shows that the community dynamics of beach wrack colonizers affect how it is degraded, and that the presence of large herbivores like amphipods contributes to the degradation of wrack and thus its integration into the beach ecosystem food web.